Why impedance was increased in the last interrogation when output voltage was increased to 3.0 V ?
That’s an important observation—and it suggests a dynamic interaction between output voltage, myocardial tissue response, and possibly electrode-tissue interface changes. Let’s analyze why this happens:
Impedance (Z) is not simply a static resistor in the heart; it involves complex bioelectric properties influenced by the voltage applied and the state of surrounding tissue.
When you increase output voltage, particularly above certain thresholds, the electrical field may:
Activate a broader, less conductive area of fibrotic or scar tissue.
Increase the effective path length of current, leading to a higher measured impedance.
Higher voltages can create electroporation-like effects (increased cell membrane permeability), causing transient changes in the conductivity of the surrounding tissue.
Chronic fibrosis or encapsulation leads to less conductive collagen tissue. When you increase voltage, the pacemaker “sees” more of this poor-conductivity material, increasing the measured impedance.
Biological tissues don’t behave like linear resistors.
At higher voltages, ionic channels in tissue saturate, and the electric field may penetrate less conductive or partially insulated areas, raising impedance.
Although it’s tempting to expect that higher voltage lowers impedance (as in metallic circuits), in biological systems, high voltages often unmask poor conductivity areas rather than improve conduction.
If impedance increases with higher output voltage and capture is still marginal, it strongly suggests that:
There is significant fibrotic encapsulation around the electrode.
The electrode-tissue interface is deteriorating.
Simply increasing voltage may worsen battery consumption without improving long-term capture stability.
Conduct a Threshold Test Across Multiple Voltages and Body Positions.
Check if there’s a consistent pattern of impedance rising with output voltage.
Monitor Battery Consumption Closely.
If output is consistently at 3.0 V or higher, and impedance is still rising, battery depletion will accelerate.
Plan for Potential Device Revision.
Consider evaluating the feasibility of Aveir CSP (Conduction System Pacing) at a new site to bypass fibrotic myocardium.